A diaphragm in a conventional loudspeaker vibration system usually employs a structure formed by bonding multiple resin material layers, but such structure of diaphragm formed by bonding multiple layers of material is apt to cause non-uniformity of thickness of the diaphragm so that the uniformity of the diaphragm is undesirable. As an improvement, the material of the diaphragm may be changed into silicon rubber membrane. A layer of silicon rubber membrane can satisfy needs of the product, so the diaphragm made from such material exhibits good uniformity. During practical application, a rigid dome part is usually disposed on the silicon rubber membrane to improve an acoustic performance of the loudspeaker. However, the diaphragm of the silicon rubber material is softer and more compliant than the diaphragm made of multiple layers of resin materials, and furthermore, transition of combination of the silicon rubber membrane and the rigid dome part is undesirable, thus it is apt to cause distortion and sensitivity is rather low. Therefore, it is necessary to improve the diaphragm made of such silicon rubber material to enhance the performance of the diaphragm of such material, reduce distortion of the diaphragm, and boost its sensitivity.